Screen conductance & utilization: the shaker’s performance ceiling

The shaker is the first and most important removal stage — and its performance is set by two numbers most crews never read: how fine it cuts, and how much fluid it can flow. API RP 13C puts both on the screen label. Read them right and you set the whole system’s ceiling. Read them wrong and you either blind the screen or flood the shaker.

The two numbers on the label

Under API RP 13C (internationally ISO 13501), every compliant screen carries two required values: the cut point as an API number (its D100 separation) and the conductance in kD/mm (its flow capacity). The old “mesh” count is obsolete — oblong and multi-layer screens made it meaningless. These two numbers are how you actually compare screens.

Cut point — how fine it removes

The API number reflects the D100 cut: the size above which essentially all particles are retained. A finer cut removes more drilled solids — but generally flows less fluid. This is the central trade-off of screen selection: go as fine as you can without running out of flow capacity for your rate and solids load.

Conductance — how much it flows

Conductance, in kilodarcies per millimetre, describes how easily fluid passes through a unit area of screen. All else equal, the higher-conductance screen processes more flow. It’s the number that decides whether a given screen can keep up with your flow rate — or whether the shaker will pool and run mud over the end.

Non-blanked area — the working surface

The non-blanked area (NBA) is the net unblocked screen area actually available to pass fluid. It’s not always on the label, but it matters: more usable area means more handling capacity. Two screens with the same cut point can perform very differently if one has far more working surface than the other.

Utilization — is the whole screen working?

A screen only performs if its surface is actually being used. Watch for a dry beach that’s too long (flow capacity wasted), pooling to the end (overloaded or too fine), and blinding or blanking (apertures plugged by near-size particles). Poor utilization means you paid for cut and conductance you’re not getting — the most common quiet performance loss on the rig.

The label describes — it doesn’t predict

One honest caveat from API RP 13C itself: the label describes the screen, it does not predict rig-site performance. Real performance depends on the whole picture — shaker model, motion and G, fluid, flow rate and solids loading. The label lets you compare screens fairly; the rig still decides what you actually get.

Put it to work

If you’re unsure whether your screens are sized right for your flow and solids load, a remote review can match cut point and conductance to your shakers and hole sizes.

Related reading

Grounded in API RP 13C (ISO 13501) and field shaker practice. Screen selection depends on shaker, fluid, flow and loading — treat as engineering guidance.